Manchester Memoirs, Vol. Ixiv. (1920), No. 3 3 



conveniently indicated the course of the well-known cyano- 

 hydrin formation. It must be emphasised, however, that in 

 attaching the — and + signs to the oxygen and carbon atoms 

 no hvpothesis is invoked, nor is it necessarv or even desirable 

 to assume that electrical charges are developed on these two 

 .atoms (except perhaps at the actual instant of chemical 

 change). The signs are applied, in the first instance, merely 

 as expressing the relative polar characters which the two atoms 

 seem to display at the instant of the chemical change in 

 question. In this respect the writer's views differ from those 

 of Frv and others, and agree with those of Robinson. 



The aldol reaction, in which compounds containing the 

 groups >CH-CO-, >CH-N0 2 , >CH - CX, etc., 1 can 

 replace the hydrogen cyanide in the addition process pictured 

 in the paragraph immediately preceding, at once suggests 

 that the hydrogen atom in these groupings has an enhanced 

 positive polar character relatively to the carbon atom on 

 which it is situated, and accordingly the writer expresses this 

 by attaching a + and a - sign to these two atoms respec- 

 tively. Combining this with the expression already developed 

 for the carbonyl group, there is obtained the scheme : 



H I 



>C-C=0 



— + - 



It may now be noted that this fusion suggests a property 

 of the whole system which was not taken into consideration in 

 deducing the signs for the two parts, and which, if absent, 

 would render it impossible to justify the use of the scheme 

 .as a whole ; this property concerns the two carbon atoms, 

 which are here necessarily shown as having opposite polarities 

 with respect to one another, and in the same sense as with 

 the hydrogen atom and the carbon atom on the left. Fortunately 

 there is plenty of evidence in favour of the existence of latent 

 polarisation in a pair of carbon atoms situated as in the above 

 scheme ; thus hydrolysis of such a complex usually if not 

 invariably takes place as follows : — 



I + - + - I 



>CH - C = O +H-OH-* >CHH + HOC = O. 



- + - - + 



Significant too are the properties of aP-un saturated ketones, 



